Super Clustering Google

OK, here's an unusual Google search result. With my preferences set to display 100 results at a time, I ran a search powells books to see if it would use the plus box. Google only displayed the first four of about 962,000 (a wildly inaccurate number, but certainly there should be more than 4). So what happened? I changed the number to be displayed to ten, and Google gave ten results. When I switched back to display 100, I more than quadrupled my retrieval with 18! Switching from Firefox 2 to IE 7 to avoid cookie effects, I still just got 18.

Of course I can click on the link in that message at the bottom of the page: "In order to show you the most relevant results, we have omitted some entries very similar to the 18 already displayed. If you like, you can repeat the search with the omitted results included." That would uncluster the results and display the first 100 results, along with another wildly inaccurate estimate of "about 2,810,000" total hits. The screen shot below shows the first iteration with only the 4 hits. Try it yourself to see how many you get. At least the first hit is always for Powells.